Do you trust your port extension/E-delay?

[brandon7861]

I've been spending a little time measuring cans with my nanoVNA. Often times, my VNA is calibrated right at the port, and when I use a small 8" coax jumper to a part soldered to an SMA, I usually just port extend/e-delay to the end of the jumper.

I always thought something was off because the delay needed to get the marker to the high z point was always way bigger than logically necessary, so I finally did some comparisons and found that I should not be trusting the e-delay feature. If I calibrate to the end of the coax, I get good results, but if I e-delay, the readings are both high and no amount of delay will make both the R and X match what the coax OSL shows. I can get both R and X close changing the delay, but one or the other ends up being 1-15 ohms off. The numbers I get with the OSL at the end of the coax match a different VNA I have, so I am confident that much is right.

I did turn the output power down as low as it would go, found that necessary to get good readings on the siglent vna too. Currently at -13dBm output.

Mine is a nanoVNA-F 4.3" HW2.2 with firmware 0.2.1 by BH5HNU. I did search around, but there are so many firmwares, I don't know what to try. I think I have the latest that is specifically for this unit.

Anyone else have this issue with their nano? Anyone got a fix that might work for mine?

 

[Cable Guy]

Watching in anticipation as I've only really used my nanovna to check and tune antennas. I just got a tinysa ultra plus and have been looking at ways to more fully utilize these great tools. I'd love to see a video of how you set up your vna and check the cans. #stilllearning

 

[brandon7861]

I'd love to see a video of how you set up your vna and check the cans. #stilllearning

I basically set my vna to the frequency of interest in CW mode (not sweeping) at the lowest power setting, then calibrate to the end of my test cable then attach the can using an sma soldered directly to the legs. I remove the slug, note the reading, then peak the slug and note that reading. That tells me the Xl range and Q so I know what to expect when using it in other circuits.

Why was I doing that? Because dss56 has some stubborn crystals coming my way and I planned on using a SSB tuning coil from a DX2547 (L22) to try to pull it down the necessary amount if pulling it up don't work out.

To that end, I was just playing with simsmith. I was thinking, if I measure the crystal parameters, I could model it ahead of time and see about what it would take to move it to where I want it. Right now, for fun, I am using the crystal frequency and parameters listed in W2AEW's video #319 at timestamp 14:48 to see what a trim cap or inductor would do his crystal in the software. More importantly, I wanted to know if that model lines up with the 47pF trim freq shown in the G3UUR method from earlier in that same video. The answer is yes, and I'm kinda excited about that.

My next step is to measure the parameters of a crystal that I have and see if I can accurately predict the shift from an inductor. For a long time, I wanted to know how they choose those inductor values at the SSB oscillators, and now I think I know.

With a few measurements ahead of time, it may be possible to know exactly what it takes to put the crystal where you want it and that is something i want to be able to accurately ballpark without guessing. #stilllearning for sure!

 

[brandon7861]

EDIT: I just effed this post up. Was thinking I was starting a new one and somehow I edited over the previous one. dang it.

The links I had are here
Measuring inductors:


simsmith crystal stuff


I was just trying to say that it worked. I measured a 6.1704MHz crystal and it allowed me to get really close to cap and inductor values. If I clean up the model for the oscillator effects, it will be right on.

 

[Cable Guy]

EDIT: I just effed this post up. Was thinking I was starting a new one and somehow I edited over the previous one. dang it.

The links I had are here
Measuring inductors:


simsmith crystal stuff


I was just trying to say that it worked. I measured a 6.1704MHz crystal and it allowed me to get really close to cap and inductor values. If I clean up the model for the oscillator effects, it will be right on.

That's great Brandon, I appreciate you taking the time to make that video. You explained what I wanted to know about setting up the vna. I need to plug other things into mine and play around with it some. That simsmith app is great too.